NUEROPHYSIOLOIGY: NERVE FUNCTION

About Nerves and AP and synapse

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NUEROPHYSIOLOIGY: NERVE FUNCTION
Membrane Potential- all cells have a resting membrane potential, membranes are polarised more negative on the
inside than the outside.
HOW IS RESTING MEMBRANE POTENTIAL GENERATED
ICF has high K+
ECF has low K+ and high Na+
ICF anions are mainly proteins
ECF anions are mainly Cl-
HOW DO IONS MOVE ACROSS CELL MEMBRANES
Through ion channels
1. PASSIVE OR LEAKAGE CHANNELS ­ are always open
2. ACTIVE OR GATED CHANNELS ­ can be open or closed
3. CHEMICAL OR LIGAND GATED CHANNELS ­ controlled by neurotransmitters
4. VOLTAGE GATED CHANNELS ­ responding to changes in membrane potential
5. MECHANICCALLY GATED CHANNELS ­responding to physical deformation
DEPOLARISATION IS WHEN THE CELLS BECOMES MORE POSITIVE by an influx on Na+ into the cell which causes a spike
in voltage. When this reaches 40mV the k+ channels open and the sodium channels close causing re-polarisation.
ACTION POTENTIALS are runaway de-polarisation which produce nerve impulses; they are caused by changes in
membrane permeability to Na+ and k+.
PHASES OF ACTION POTENTIAL
1. RESTING PHASE- cell maintain resting membrane potential at -70mV
2. DEPOLARISING PHASE ­ Na+ gates open causing depolarisation, depolarisation is only reached when
threshold potential is reached.
3. RE-POLARISING PHASE- Na+ gates close and K+ gates open causing re-polarisation.
4. HYPER-POLARISATION ­ Repolarisation overshoots, sodium potassium pumps then restore ionic balance.
Any stimulus reducing the membrane potential 10-50mV will set in action a chain of events in which positive
feedback will increase the influx of Na+ and create an action potential.
Resting potential ­ the membrane potential at euibrimum -70mV.
Threshold- the membrane potential at which runaway depolarisation commences.
Depolarisation ­ the movement of the membrane potential away from the resting potential.
Repolarisation ­ movement of the membrane potential towards the resting potential.
Hyperpolarisation ­ movement of the membrane potential below the resting potential.
EVENTS AT THE SYNAPSE
AP arrives at the synaptic knob causing Ca2 to enter the cell
High Ca2 concentration causes synaptic vesicles to move to the synaptic cleft and release the transmitter
Neurotransmitter diffuses across synapse and binds to receptors on post-synaptic membrane.
Ion gates open causing change in membrane potential
Neurotransmitter is removed from the synaptic cleft.
Takes time and known as the synaptic delay.
CHEMICAL SYNAPSE
Pre-synaptic axon terminal knob containing synaptic vessels.

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Synaptic cleft fluid filled space between the pre-synaptic and post synaptic cells
Post synaptic membrane containing receptors for the neurotransmitter.
NEUROTRANSMITTERS
Acetylcholine
Noradrenaline
Three factors which determine the rate of a nerve impulse
Myelination
Thickness of nerve
Temperature
What is meant by the terms?
Excitatory Postsynaptic Potential ­ when the post synaptic
membrane potential depolarises.
Inhibitory Postsynaptic Potential ­ when the post synaptic
membrane potential hyperpolarises.
Temporal Summation- rapid firing of neurons one after the
other.…read more

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